• Journal of the military operations research society of Korea
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• v.16 no.1
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• pp.113-129
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• 1990

This paper presents the simulation model to decide the mean size of cannibalization aircraft (MSCA) under steady state when an airbase makes use of cannibalization to support the spare parts of an airfleet. In this model, the essential factors such as mission requirements, mission time, failure time, repair time, repair capability, inventory policy, cannivalization rule are considered. The model is constructed with above factors and actual airbase operating rules for a basis. Because of the tangled interdependencies among the each factors, it is inevitable to construct the model by the simulation technique. The mission and support system of the airbase is considered as a closed queueing network with a finite number of unit The troubled aircrafts are repaired in accordance with the priorities that are determined by their repair times. The illustrative example of the model, using the actual data of xx-airbase, is presented. The model would be a useful tool not only to determine the MSCA and the size of scheduled maintenance aircraft but to evaluate the NORS (not operationally ready supply) rate and the availability of an airfleet.

• International Journal of Reliability and Applications
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• v.12 no.1
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• pp.49-60
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• 2011

The geometric process (GP) has been widely used for modeling failure and repair time sequences of repairable systems. The GP is mathematically tractable but restrictive in reliability applications since it actually assumes that the mean function of inter-failure times sequence asymptotically decreases to zero; and the mean function of successive repair times sequence asymptotically increases to infinity. This is generally unrealistic from an engineering perspective. This paper presents three extended GP models for modeling reliability deterioration and improvement (or growth) process. The extensions maintain the advantage of mathematical tractability of GP model. Their usefulness and appropriateness are illustrated with three real-world examples.

• Clinics in Shoulder and Elbow
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• v.19 no.2
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• pp.60-66
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• 2016

Background: Management of massive rotator cuff tears can be challenging because of the less satisfactory results and a higher retear rate regardless of the use of open or arthroscopic repair technique. Methods: We retrospectively analyzed 102 cases of massive rotator cuff tear treated with either open or arthroscopic repair. Open repair was performed in 38 patients; and arthroscopic repair, in 64 patients. The mean age at the time of surgery was 59.7 years in the open group and 57.6 years in the arthroscopic group. Results: The Constant score increased from the preoperative mean of 55.9 to 73.2 at the last follow-up in the open repair group and from 53.8 to 67.6 in the arthroscopic repair group (p<0.001 and <0.001, respectively). The University of California at Los Angeles (UCLA) score increased from a preoperative mean of 17.7 to 30.8 at the last follow-up in the open group and from 17.5 to 28.7 in the arthroscopic group (p<0.001 and <0.001, respectively). No statistically significant difference in the Constant and UCLA scores was observed between the two groups at the last follow-up (p=0.128 and 0.087, respectively). Retear was found in 14 patients (36.8%) in the open group and 39 patients (60.9%) in the arthroscopic group (p=0.024). Conclusions: Open and arthroscopic repairs of massive rotator cuff tears may provide satisfactory clinical results with no significant difference. However, a significantly lower retear rate was observed for the open repair group compared with the arthroscopic repair group.

• Journal of Korean Foot and Ankle Society
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• v.22 no.2
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• pp.68-73
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• 2018

Purpose: This study compared the clinical outcomes of open repair, percutaneous repair, and minimal incision repair by Achillon in ruptured Achilles tendon. Materials and Methods: The outcomes of 12 patients with open repair (group 1), 8 patients with percutaneous repair (group 2), and 10 patients with minimal incision repair by Achillon (group 3) from February 2013 to March 2016 were analyzed retrospectively. The postoperative clinical evaluations were done by the American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score, Arner-Linholm scale, mid-calf circumference difference, one-leg heel raise difference, visual analogue scale (VAS) for postoperative scarring, time to return to work, and complications. Results: No significant difference in the AOFAS ankle-hindfoot score, Arner-Linholm scale, and time to return to work was observed among three groups (p=0.968, 0.509, and 0.585). The mean differences in the mid-calf circumference in groups 1, 2, and 3 were 1.09, 0.73, and 0.58, respectively; groups 2 and 3 were significantly higher than group 1 (p=0.002). In addition, the mean VAS scores for postoperative scarring in groups 1, 2, and 3 were 7.0, 9.1, and 9.1, respectively; groups 2 and 3 were significantly higher than group 1 (p=0.001). The mean differences in one-leg heel raising in groups 1, 2, and 3 were 2.03, 1.91, and 1.33, respectively; group 3 was significantly higher than groups 1 and 2 (p=0.010). The complications encountered were one case of deep infection in group 1 and one case of sural nerve hypoesthesia in group 2. Conclusion: Minimal incision repair by Achillon is recommended as an effective surgical treatment for Achilles tendon rupture because it minimizes the risk of complications, leads to an improved tendon strength and healing, and achieves cosmetic satisfaction.

• Journal of the Korean Data and Information Science Society
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• v.14 no.4
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• pp.997-1005
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• 2003

In this paper, the problem of determining optimal burn-in time is considered under a general failure model. There are two types of failure in the general failure model. One is Type I failure (minor failure) which can be removed by a minimal repair and the other is Type II failure (catastrophic failure) which can be removed only by a complete repair. In this model, when the unit fails at its age t, Type I failure occurs with probability 1 - p(t) and Type II failure occurs with probability p(t), $0{\leq}p(t)\leq1$. Under the model, the properties of optimal burn-in time maximizing mean time to the catastrophic failure during field operation are obtained. The obtained results are also applied to some illustrative examples.

• Journal of Chest Surgery
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• v.48 no.5
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• pp.328-334
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• 2015

Background: There have been a number of studies on mitral valve replacement and repeated percutaneous mitral balloon valvotomy for mitral valve restenosis after percutaneous mitral balloon valvotomy. However, studies on mitral valve repair for these patients are rare. In this study, we analyzed postoperative outcomes of mitral valve repair for mitral valve restenosis after percutaneous mitral balloon valvotomy. Methods: In this study, we assessed 15 patients (mean age, $47.7{\pm}9.7years$; 11 female and 4 male) who underwent mitral valve repair between August 2008 and March 2013 for symptomatic mitral valve restenosis after percutaneous mitral balloon valvotomy. The mean interval between the initial percutaneous mitral balloon valvotomy and the mitral valve repair was $13.5{\pm}7years$. The mean preoperative Wilkins score was $9.4{\pm}2.6$. Results: The mean mitral valve area obtained using planimetry increased from $1.16{\pm}0.16cm^2$ to $1.62{\pm}0.34cm^2$ (p=0.0001). The mean pressure half time obtained using Doppler ultrasound decreased from $202.4{\pm}58.6ms$ to $152{\pm}50.2ms$ (p=0.0001). The mean pressure gradient obtained using Doppler ultrasound decreased from $9.4{\pm}4.0mmHg$ to $5.8{\pm}1.5mmHg$ (p=0.0021). There were no early or late deaths. Thromboembolic events or infective endocarditis did not occur. Reoperations such as mitral valve repair or mitral valve replacement were not performed during the follow-up period ($39{\pm}16months$). The 5-year event-free survival was 56.16% (95% confidence interval, 47.467-64.866). Conclusion: On the basis of these results, we could not conclude that mitral valve repair could be an alternative for patients with mitral valve restenosis after percutaneous balloon mitral valvotomy. However, some patients presented with results similar to those of mitral valve replacement. Further studies including more patients with long-term follow-up are necessary to determine the possibility of this application of mitral valve repair.

• Journal of the Korean Operations Research and Management Science Society
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• v.17 no.2
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• pp.123-130
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• 1992

The model of k-out-of n : G repairable system with identical components is extended to a repairable system with n different components. The objective is to analytically derive the mean time of the busy period for a k-out-of-n : G system with unrestricted repair. Then, the lower and upper bounds on the average time of the busy period of the n-component system with restricted repair are also shown.

• International Journal of Reliability and Applications
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• v.11 no.2
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• pp.123-138
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• 2010

This paper investigates a mathematical model of a system composed of two non-identical unit parallel system with common-cause failure, critical human error, non-critical human error, preventive maintenance and two type of repair, i.e. cheaper and costlier. This system goes for preventive maintenance at random epochs. We assume that the failure, repair and maintenance times are independent random variables. The failure rates, repair rates and preventive maintenance rate are constant for each unit. The system is analyzed by using the graphical evaluation and review technique (GERT) to obtain various related measures and we study the effect of the preventive maintenance preventive maintenance on the system performance. Certain important results have been derived as special cases. The plots for the mean time to system failure and the steady-state availability A(${\infty}$) of the system are drawn for different parametric values.

• Journal of Chest Surgery
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• v.24 no.2
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• pp.115-122
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• 1991

From April 1986 to December 1989, 25 infants under the age of 12 months with tetralogy of Fallot were operated on. Age ranged from 3 to 12 months[mean 8.9$\pm$4.9 months] and mean body weight was 7.8$\pm$ 2.6kg. All the patients were deeply cyanotic, 12 of them experienced anoxic spell. Transannular patch was laid down in 19 patients, in 7 of them monocuspid patch was utilized. Postrepair P RV/LV was measured at operation room in 17 patients[mean 0.48$\pm$0. 14]. Hospital mortality was 20Yo. Causes of deaths include right ventricular failure and low cardiac output. The mortality was closely related with patient`s age and body surface area at operation. Also higher mortality was noticed in patients having major associated anomaly or previous palliative operation, preoperative management with propranolol and transannular repair. 18 patients were followed up for 12 to 50 months with a mean follow-up time of 24 months after operation. There were no late deaths and late ventricular arrhythmia or congestive heart failure was not detected as yet. Redo operation was performed in one case because of residual pulmonic stenosis. Considering several advantages of early primary repair, primary repair of symptomatic infants with tetralogy of Fallot should be encouraged despite somewhat high mortality rate as yet and better results could be anticipated along with improvement of myocardial protection method and postoperative care.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.691-698
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• 1996

This paper propose a procedure to estimate the system lifetime distribution using simulation method in a parametric framework and also develop the criterion for terminating the simulation. We assume that a system is composed of many components whose lifetime and repair time distributions are general, and repair of each component is imperfect or not. General simulation algorithms can not be adopted for this case, due to the dependency of successive operating times and the discontinuity in base line intensity function of failure process. Then we propose algorithms for generating failure times subject to imperfect repair. We develop the event time tracking logic for identifying the system failure time, and also develop the criterion for terminating the simulation. Our procedure is composed of two phases. The first phase of the procedure is to generate the system failure times from the inputs. The second phase is to estimate the lifetime distribution of the system. The best model is selected by a fully automated procedure among well-known parametric families, and the required parameters are estimated. We give examples to show the accuracy of our procedure and the effect of repair effect of components to system MTTF(Mean Time To Failure).